Hydro-dynamic fluid bearing device and manufacturing method of the same

ABSTRACT

A novel hydro-dynamic fluid bearing device is herein disclosed which comprises a cylindrical shaft, a substantially cylindrical bearing member for axially supporting the shaft rotatably in a cylindrical hole having a bottom surface, a supporting member fixed on one side of the shaft and the bearing member, and a rotation member fixed on the other side of the shaft and the bearing member and rotatably supported on the supporting member, grooves for generating hydro-dynamic fluid being formed on at least one of the outer peripheral surface of the shaft and the inner peripheral surface of the cylindrical hole of the bearing member, wherein the bearing member is made of a resin material, and the outer peripheral surface of the substantially cylindrical portion is fixed to an annular reinforcing member having a higher rigidity than the bearing member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hydro-dynamic fluid bearing device,more detailedly, to a hydro-dynamic fluid bearing device of a spindlemotor for an information system, an audio/visual system or the like,especially, to a hydro-dynamic fluid bearing device of a spindle motorsuitable for an optical disk system or a magnetic disk system, and alsoto a method of making a bearing member used in such a device.

2. Related Background Art

Sliding bearings, ball bearings or hydro-dynamic fluid bearings areconventionally used in information systems such as LBPs (laser beamprinters) and CD-ROM drive systems. Bearing devices in DVD (digitalvideo disk) systems, which are new information systems, are planned toemploy such bearings and some of them are practically utilized.

Bearing devices for laser beam printers, CD-ROM drive systems or thelike, require high rigidity, low friction and good durability.

However, conventional bearing devices have the following problems.

In a bearing device using a sliding bearing, a thrust bearing isrequired in addition to a radial bearing. The number of parts thusincreases. Besides, shaft run-out is large. Such shaft run-out is apt tooccur in accordance with the size of the gap between a radial bearingand a shaft. Furthermore, wear resistance is bad. Abrasion is apt to beheavy in particular when the rotational speed is high.

In a bearing device using a ball bearing, the ball bearing itself isexpensive. Furthermore, rotation unevenness and vibration are apt tooccur.

In a bearing device using a hydro-dynamic fluid bearing (made of metal),a thrust bearing is required in addition to a radial bearing. The numberof parts thus increases. Besides, wear resistance is low becauseabrasion is easy to occur due to contact at the time of start or stop.Furthermore, the manufacturing cost is high because of the formation ofgrooves for generating hydro-dynamic fluid and the highly accuratefinish of a bearing surface.

Considering the above problems, the present inventor et al. proposed ahydro-dynamic fluid bearing using a bearing member made of resin whichis superior in anti-friction and wear resistance, and can be formed inone body by injection molding, and the cost of which is low. Such abearing device, however, has the following new problem. Since therigidity of resin is lower than that of metal, the bearing member madeof resin is displaced (elastically deformed) when unbalance quantity(radial load) is large.

In recent years, the rotational speeds of fluid bearing devices forspindle motors of optical disk systems or magnetic disk systems are tendto increase because of the demand of the high speed transmission ofdata. In a supporting bearing of such a spindle motor, the influence ofcentrifugal force at a high speed rotation due to the unbalance of arotation member becomes larger.

FIG. 12 shows a cross-sectional view of a prior art bearing device. Arotation member comprises a shaft 130, a disk attachment flange 131 anda rotor 133. The shaft 130 is rigidly inserted in the disk attachmentflange 131. The rotor 133 is fixed to the lower surface of the diskattachment flange 131.

A support member for supporting the shaft 130 comprises a stator 134, abase 135, a bearing member 136 and a steel ball 137. For operating as aradial hydro-dynamic fluid bearing, grooves for generating hydro-dynamicfluid are formed in a cylindrical radial bearing surface 136a of thebearing member 136. The bearing member 136 is firmly inserted in thebase 135. The steel ball 137 is tightly inserted in the lower endportion of the bearing member 136. The steel ball 137 operates as athrust bearing. The stator 134 is firmly inserted in and fixed to thebearing member 136.

The operation will be described. When the stator 134 is electrified, arotating magnetic field is generated. The rotor 133 thereby rotatestogether with the shaft 130 and the disk attachment flange 131. Thepressure of a lubricant in a radial bearing gap thereby increasesbecause of a pumping effect by the grooves for generating hydro-dynamicfluid formed in the radial bearing surface 136a. The rotor 133 thusrotates in non-contact state between the radial bearing surface 136a anda radial receiving surface 136b which were initially in contact witheach other.

In the thrust bearing, a sliding bearing is formed by point contactbetween a thrust bearing surface 130a of an end surface of the shaft 130and a thrust receiving surface 137a. The lubricant is disposed betweenthe thrust bearing surface 130a and the thrust receiving surface 137a.The rotor 133 thus rotates in point contact state through the lubricant.

Synthetic oils having good boundary lubrication properties were studiedfor such a lubricant. Particularly, load capacities of the above radialand thrust bearings are in proportion to the viscosity of a lubricantused. Since the change of the viscosity of synthetic oil with the changeof temperature are large, an oil which meets the necessary load capacityat a high temperature, largely increases in its viscosity at a lowtemperature so as to increase the dynamic torque of a bearing.Contrarily, if an oil having the viscosity where the optimum dynamictorque of a bearing is obtained at a low temperature, is chosen, theviscosity decreases at a high temperature so that the load capacitybecomes insufficient. Because synthetic oils are inferior in theirtemperature-viscosity properties in general, the diameter of the shaftwas 1.5 mm for lowering the torque of the bearing device, or the radialbearing gap between the radial bearing surface 136a and the radialreceiving surface 136b was narrowed to 3 μm for insuring the necessaryload capacity.

When the rotational speed of a bearing device becomes higher, however,the centrifugal force becomes larger due to the unbalance at the time ofmounting a disk. The flexural rigidity of the shaft thus lacks, causinga problem that the run-out range of a rotational body becomes larger.Besides, in bearing devices, it is required to lower the torque at a lowtemperature because of a demand for saving the electric power to thedevice.

As another prior art, a dynamic air pressure bearing having aconstruction schematically shown in FIG. 13 is, used in a scanner motorfor polygon mirror in a laser printer which is an information system. Ashaft 202, in the outer surface of which grooves 203 for generatinghydro-dynamic fluid are formed, is inserted in a sleeve 201 which is acylindrical member. A radial dynamic air pressure bearing for supportingthe sleeve 201 in the radial direction to the shaft 202 is formed byutilizing an air pressure which is generated by the grooves 203 forgenerating hydro-dynamic fluid at the relative rotation of the sleeve201 and the shaft 202. An end opposite to an end through which the shaft202 is inserted, is closed with a thrust plate 204. A pair of permanentmagnets 205 and 206 is mounted on the end surface of the shaft 202 andthe inner surface of the thrust plate 204 opposite to the former,respectively, so as to repel each other. A thrust magnetic bearing forsupporting the sleeve 201 in the axial direction to the shaft 202 isformed by the repulsion between the permanent magnets 205 and 206.

In the dynamic air pressure bearing as shown in FIG. 13, however,because of the construction where air of low viscosity and littlelubrication is used as a lubricant fluid, it is required to finish invery high accuracy the bearing surfaces such as the inner surface of thesleeve 201 and the outer surface of the shaft 202. Besides, the goodslidability of those bearing surfaces must be insured. For thesepurposes, after the inner surface of the sleeve 201 made of structuralsteel is ground or honed, the inner surface is coated with a compositeplating in which polyethylene fluoride resin such as Teflon (tradename), that is, polytetrafluoroethylene is impregnated in nickel. Theinner surface is again ground or honed to insure the dimensionalaccuracy. On the other hand, the grooves for generating hydro-dynamicfluid must be formed by etching in the outer surface of the shaft 202made of stainless steel which cooperates with the sleeve 201.

As for the sleeve 201, because a thick plating can not be formed, twotimes of grinding or honing are required. There are problems that themanufacturing cost increases in addition to increasing the cost forplating. As for the shaft 202, there are problems that the process ofetching is complex and has need of a long time and the cost increases.Since the magnetic bearing using the repulsion between the permanentmagnets 205 and 206 is employed for the thrust bearing, there areproblems that the construction is complex, the number of parts increasesand the cost for manufacturing the whole of the bearing is high.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide ahydro-dynamic fluid bearing device of high rigidity, low friction andgood durability by reinforcing a bearing member made of resin with anannular member having higher rigidity than the bearing member made ofresin.

It is another object of the present invention to provide a motorincluding a hydro-dynamic fluid bearing device of the decreased numberof parts and low cost by using an annular member as a rotor or a statorof the motor.

For solving the above-described problems, in a hydro-dynamic fluidbearing device according to the first aspect of the present invention, abearing member made of resin has a cylindrical radial bearing surface ina cylindrical hole, the radial bearing surface has grooves forgenerating hydro-dynamic fluid, and the bearing member is reinforced bythe manner that the outer surface of the bearing member is fixed to anannular member which has the higher rigidity than the bearing member.

The outer surface of the bearing member may be reinforced by the mannerthat its both end portions in the axial direction are mounted to theannular member. The annular member may be a rotor included in the drivestructure of the motor. The annular member may be a stator included inthe drive structure of the motor.

Since the bearing member is reinforced by the annular member having thehigher rigidity than the bearing member, a lack of the rigidity of thebearing member made of resin is complemented so that the bearing membermade of resin is not displaced even in the case of the large unbalancequantity.

A motor of simple structure, the small number of parts and low cost canbe obtained if the annular member is utilized as a rotor or a stator ofthe motor.

It is an object of a hydro-dynamic fluid bearing device according to thesecond aspect of the present invention to provide a hydro-dynamic fluidbearing device wherein the flexural rigidity of a shaft is to beimproved and the problem that the run-out range of a rotational bodybecomes larger is solved, and the dynamic torque is to be decreased at alow temperature, by aiming at the shape of the bearing device and alubricant.

A hydro-dynamic fluid bearing device is to provide a hydro-dynamic fluidbearing device in which a cylindrical radial bearing surface of abearing member is opposite through a radial bearing gap to a radialreceiving surface of a shaft, and grooves for generating hydro-dynamicfluid are formed in at least one of the radial receiving surface and theradial bearing surface, characterized in that the diameter of the shaftis 2 to 5 mm, a fluoric oil the kinematic viscosity of which is 20 to200 cSt at 40° C. is used as a lubricant in the radial bearing gap, andthe radial bearing gap is 3.5 to 10 μm.

Since the diameter of the shaft is 2 to 5 mm, the flexural rigidity ofthe shaft is improved. Within this range, it is possible to decrease therun-out range of a rotation member which is a rotational body. If thediameter of the shaft is larger than 5 mm, the dynamic torque becomestoo large.

As a lubricant, a fluoric oil where the increase of torque at a lowtemperature is small is used. Particularly, when a fluoric oil which hasgood temperature-viscosity properties and the kinematic viscosity ofwhich is 20 to 200 cSt at 40° C., is used, and the radial bearing gapbetween the radial bearing surface and the radial receiving surface is3.5 to 10 μm, the appropriate dynamic torque is obtained at a lowtemperature.

By this feature, it becomes possible to meet a demand of saving theenergy of a bearing device. At a low temperature, since the energy foroperating a bearing device had to be increased due to an increase of theviscosity of a lubricant with a difference from the viscosity propertiesof the lubricant at a normal temperature, there was a requirement of theenergy which is not required at the normal temperature. In the presentinvention, it becomes possible to drive a bearing device without usingsuch extra energy.

As for properties of a fluoric oil as a lubricant, when the kinematicviscosity is less than 20 cSt at 40° C., the dynamic torque becomessmall but the load capacity becomes insufficient at a high temperature.When the kinematic viscosity is more than 200 cSt at 40° C., the loadcapacity becomes large but the dynamic torque becomes too large at a lowtemperature. For exhibiting fully the effect of the present invention,therefore, the use within the range of 20 to 200 cSt at 40° C. ispreferable as described above.

When a fluoric oil as a lubricant includes perfluoropolyether havingcarboxylic acid at its termination which is mixed by 0.1 to 10 wt. %,boundary lubrication properties and leakage properties of the lubricantare further improved.

But, when a fluoric oil includes perfluoropolyether having carboxylicacid at its termination of less than 0.1 wt. %, the boundary lubricationproperties and the leakage properties of the lubricant become inferior.When a fluoric oil includes perfluoropolyether having carboxylic acid atits termination of more than 10 wt. %, physical properties of thefluoric oil become inferior and it becomes difficult to obtain theadequate dynamic torque at a low temperature.

When the radial bearing gap between the radial bearing surface and theradial receiving surface is less than 3.5 μm, the dynamic torque becomeslarge at a low temperature. When the radial bearing gap is more than 10μm, the dynamic torque becomes small but the load capacity becomesinsufficient at a high temperature. For exhibiting fully the effect ofthe present invention, therefore, the radial bearing gap within therange of 3.5 to 10 μm is preferable as described above.

When the radial bearing gap is within the range of 3.5 to 10 μm, thereis an effect that the insertion of the shaft to the bearing memberbecomes easy even in the state of injecting a lubricant into the bearingmember and without forming a vent hole in the bearing member.

A cylindrical radial bearing surface disposed in the bearing member isopposite through a radial bearing gap to a radial receiving surfacedisposed in a shaft. Furthermore, a thrust receiving surface disposed inan end surface of the shaft may be opposite to a thrust bearing surfacedisposed in the bearing member.

Grooves for generating hydro-dynamic fluid may be formed in at least oneof the radial bearing surface and the radial receiving surface of thehydro-dynamic fluid bearing device. The formation of the grooves is notlimited to either the radial bearing surface or the radial receivingsurface.

When the structure of point contact between a thrust receiving surfaceand a thrust bearing surface is employed, the contact area can beconsiderably decreased so it can be attempted to decrease the dynamictorque. When the thrust receiving surface and the thrust bearing surfaceare opposite to each other through a lubricant, it is expected toimprove boundary lubrication properties and it becomes possible todecrease the abrasion between the contact surfaces. Particularly, when aconvex spherical surface is formed in the thrust bearing surface, theprocess that a steel ball constituting a thrust bearing is tightlyinserted to a bearing member can be omitted. It is thus attempted toimprove the workability of assembling.

A bearing member having a radial bearing surface and a thrust bearingsurface may be integrally formed of synthetic resin. Otherwise,differently from the integral formation, a bearing member having aradial receiving surface may be made of copper group metal such asfree-cutting brass and phosphorus bronze, and a thrust receiving memberhaving a thrust bearing surface may be formed of a plate made of wearresisting metal or ceramics. The thrust receiving member is mounted tothe bearing member. By employing this structure, it is possible tomaintain the strength of the flexural rigidity of the bearing device,and to restrain the phenomenon of generating the abrasion of the thrustreceiving member.

As the above, for obtaining the high rigidity, the little abrasion andthe good durability at the high speed operation in a hydro-dynamic fluidbearing device, in the first aspect, there was described means forrestraining shaft run-out or the like by a combination of a reinforcingmember to a bearing member mainly made of resin material. In the secondaspect, there was described means for restraining shaft run-out or thelike by a combination of the shape and a lubricant to a bearing membermade of resin material or others.

These aspects were separately described for simplifying the descriptionsince they are effective when separately used. The combination of them,however, bring on the more remarkable effect.

Next, as for a bearing member particularly made of resin material andused in the above first and second aspects, a hydro-dynamic fluidbearing member effective to the above aspects will be described as thethird aspect. Like the above first and second aspects, the third aspectwill be separately described for simplifying the description. It isneedless to say that even only the third aspect is effective to theobjects of the present invention.

A hydro-dynamic fluid bearing device according to the third aspect ofthe present invention is made by paying attention to various problems ofconventional bearing devices and its object is to provide ahydro-dynamic fluid bearing of good durability, simple process, thesmall number of parts and low cost.

For attaining the above object, the present invention is a hydro-dynamicfluid bearing characterized in that a cylindrical portion having groovesfor generating hydro-dynamic fluid in its inner surface, end a bottomportion integrally with the cylindrical portion are formed into one bodyby injection molding with resin material, the nearly central portion ofthe outer surface of the bottom portion is the portion that the resinmaterial lastly flowed in, the inside diameter of the cylindricalportion is 2 to 5 mm, the thickness of the cylindrical portion is 0.8 to2 mm, and at injection molding, the grooves for generating hydro-dynamicfluid was separated by forced drawing from a core pin which formed thegrooves for generating hydro-dynamic fluid.

When the inside diameter of the cylindrical portion is less than 2 mm,the load capacity of the bearing becomes small not to be suited for theuse as a hydro-dynamic fluid bearing. When the inside diameter is morethan 5 mm, it becomes difficult to maintain the accuracy of the insidediameter surface of the cylindrical portion. The inside diameter of thecylindrical portion is thus adequate within the range of 2 to 5 mm. Asfor the thickness of the cylindrical portion, when the thickness of theresin is less than 0.8 mm, pressure inclination is generated in theaxial direction (the longitudinal direction) at the time of injectingthe resin so that the inside diameter surface is formed in a tapershape. When the thickness is more than 2.0 mm, the influence of sinkmarks and orientation properties of the resin is considerable so thatthe roundness and the generant shape become bad. The thickness of thecylindrical portion is thus adequate within the range of 0.8 to 2 mm.

It is desirable that the resin material includes polyphenylene sulfideresin, carbon fibers and one or more fillers other than the carbonfibers, the total content of the fillers including the carbon fibers is20 to 50 wt. %, and the melt index of the resin material is 4 to 9g/min. at the temperature of 300° C. and the load of 5 kg. Instances ofother fillers than the carbon fibers are graphite, molybdenum disulfide,fluororesin, spherical silica and phenolic resin.

The nearly central portion of the outer surface of the bottom portion isthe portion that the resin material lastly flowed in a mold at injectionmolding. At injection molding, the grooves for generating hydro-dynamicfluid was separated by forced drawing from a core pin which formed thegrooves for generating hydro-dynamic fluid. Thus, no weld mark isgenerated and the mold structure becomes simple. By selecting the abovedimensions of the hydro-dynamic fluid bearing, the processing becomeseasy and the number of parts can be decreased so the hydro-dynamic fluidbearing can be manufactured at low cost.

The hydro-dynamic fluid bearing uses resin which is superior inslidability and wear resistance. The hydro-dynamic fluid bearing issuperior in durability since it is strong to impacts when touching theshaft at times of start and stop.

The hydro-dynamic fluid bearing is manufactured by injection molding. Asmolding material for the hydro-dynamic fluid bearing, one or morefillers in addition to carbon fibers are filled to polyphenylene sulfideresin. The total content of the fillers including the carbon fibers is20 to 50 wt. %. When the total content is less than 20 wt. %, moldshrinkage becomes large so that the accuracy can not be insured.Further, the strength can not also be insured. When the total content ismore than 50 wt. %, flowability becomes bad so that the accuracy can notbe insured.

The melt index is 4 to 9 g/min. (measured at the temperature of 300° C.and the load of 5 kg). When the melt index is less than 4 g/min., theflow becomes bad so the necessary accuracy can not be obtained. When themelt index is more than 9 g/min., mold shrinkage becomes large so thenecessary accuracy can not be obtained. By selecting the above wt. % ofthe fillers, it becomes possible to manufacture a hydro-dynamic fluidbearing in high accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the first embodiment of the presentinvention;

FIG. 2 is a cross-sectional view of the second embodiment of the presentinvention;

FIG. 3 is a cross-sectional view of the third embodiment of the presentinvention;

FIG. 4 is a cross-sectional view of the fourth embodiment of the presentinvention;

FIG. 5 is a cross-sectional view of the fifth embodiment of the presentinvention;

FIG. 6 is an illustrative view of a stator a part of which is cut out;

FIG. 7 is a cross-sectional view of the sixth embodiment of the presentinvention;

FIG. 8 is a cross-sectional view of the seventh embodiment of thepresent invention;

FIG. 9 is a vertically cross-sectional view of the eighth embodiment ofthe present invention;

FIG. 10A is measurement data of the roundness in a hydro-dynamic fluidbearing device of the eighth embodiment of the present invention;

FIG. 10B is measurement data of the processing accuracy in relation toshape;

FIG. 11 is a vertically cross-sectional view of the principal part of aninstance of a mold for injection molding for a hydro-dynamic fluidbearing device of the present invention;

FIG. 12 is a cross-sectional view of an instance of a prior art bearingdevice; and

FIG. 13 is a cross-sectional view of another instance of a prior artbearing device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to drawings. FIG. 1 shows a cross-sectional view of a motor 1including a hydro-dynamic fluid bearing device of the first embodimentof the present invention.

In the motor 1 of this embodiment, a bearing member 4 made of resin isintegrally formed so as to have a cylindrical radial bearing surface 6provided with grooves 5 for generating hydro-dynamic fluid in acylindrical hole 2, and a thrust bearing surface 7 which is connected tothe radial bearing surface 6. The radial bearing surface 6 is ahydro-dynamic fluid bearing surface and the thrust bearing surface 7 isa sliding bearing surface. A lubricant is disposed in the cylindricalhole 2 as a lubricant fluid. The outer circumferential surface of thebearing member 4 is fixed by adhesion to a metal housing 3 which is anannular member. A shaft 16 is inserted in the bearing member 4 so as tobe rotatable. A stator 9 is fixed to the outer circumferential surfaceof the metal housing 3. The metal housing 3 is fixed to a base (or aprint circuit board) 10 with a screw 11. The stator 9 has coils 12. Arotor 14 is disposed outside in the radial direction of the stator 9 soas to be opposite to the stator 9. The rotor 14 is fixed to the shaft 16through a yoke 13. The rotor 14 and the stator 9 constitute a drivemechanism of the motor 1 including the hydro-dynamic fluid bearingdevice.

In the hydro-dynamic fluid bearing device constructed as describedabove, since the bearing member 4 is fixed by adhesion to the metalhousing 3 which has the higher rigidity than the bearing member 4, so asto reinforce the cylindrical portion 4a of the bearing member 4, thebending displacement (bending elastic deformation) of the bearing member4 does not occur even if there is the large unbalance load in the rotor14 and the large centrifugal force (radial load) attending the rotationof the rotor (shaft) acts upon the bearing member 4.

The outer circumferential surface of the bearing member 4 may be fixedby adhesion to the metal housing 3 either through the entirety in theaxial direction of the bearing member 4 or only through the upperportion of the bearing member 4. In the case of the fixture only byadhesion at the upper portion, because a small flange 21 which is formedat a level near the bottom of the bearing member 4 is fixed to thehousing 3 by the manner that both side surfaces in the axial directionof the flange 21 is pressed in the axial direction of the bearing member4 by fastening the housing 3 to the base 10 with the screw 11, the outercircumferential surface of the bearing member 4 is fixed to the housing3 at two portions of its upper and lower portions to obtain thesufficient reinforcement for the bending displacement of the bearingmember 4.

Although the bearing member 4 made of resin is inferior in flexuralrigidity to metal, the friction is low and the wear resistance is goodand it can be manufactured at low cost by injection molding. It becomespossible to provide a hydro-dynamic fluid bearing device of highrigidity, low friction, good durability and low cost by compensating thelack of the flexural rigidity of the cylindrical portion 4a of thebearing member 4. The radial load and the thrust load can be born by onebearing member 4 having the thrust bearing surface 7 which is a convexspherical surface and the radial bearing surface 6.

FIG. 2 shows the second embodiment.

Features different from the first embodiment are that the flange 21 ofthe bearing member 4 made of resin is larger in the radial directionthan that of the first embodiment, and the base 10 is sandwiched by theupper surface of the flange 21 of the bearing member 4 and the lowersurface of a flange 20 of the housing 3, and the base 10 and the bearingmember 4 are fixed to the housing 3 with the screw 11. The bearingmember 4 may be fixed by adhesion to the annular metal housing 3 eitherthrough the entirety in the axial direction of the outer circumferentialsurface of the bearing member 4 or only through the upper portion of theouter circumferential surface of the bearing member 4, like the firstembodiment. When the screw 11 is disposed so as not to protrude in theaxial direction from the bearing member 4, there is an advantage that athin bearing device can be obtained without changing the length of thebearing member 4.

Other operations and effects are similar to those of the firstembodiment.

FIG. 3 shows the third embodiment.

Features different from the first embodiment are that the flange 21 ofthe bearing member 4 is sandwiched by the base 10 and the flange 20 ofthe housing 3, and the base 10 and the bearing member 4 are fixed to thehousing 3 with the screw 11. The number of steps for processing thehousing 3 is smaller than that of the first embodiment and the thicknessaccuracy of the flange 21 of the bearing member 4 is not required.Because the flange 21 of the bearing member 4 is directly fixed to thehousing 3, the strength of the fixture with the screw is higher thanthat of the second embodiment.

Other operations and effects are similar to those of the firstembodiment.

FIG. 4 shows the fourth embodiment.

Features different from the third embodiment are that the diameter ofthe outer circumferential surface of the bearing member 4 is smaller ata portion 4c near a cylindrical opening than at the other portion, andthe portion 4c is fixed to the annular housing 3 by adhesion or firminsertion.

Generally, when the outside diameter surface of the bearing member 4made of resin is firmly inserted, the interference of the outsidediameter affects the shrinking quantity of the inside diameter. Theshrinking quantity of the inside diameter is 80 to 100% of theinterference of the outside diameter though it varies in accordance withthe ratio of the inside diameter to the outside diameter (d/D) and thequality of the material. It is thus impossible to insure the accuracy ofthe inside diameter of the bearing member 4 made of re(sin which isrequired for a hydro-dynamic fluid bearing. Accordingly, in thisembodiment, the metal housing 3 is in contact with the portion 4c nearthe opening which is an outside diameter portion corresponding to alubricant reservoir 8 (the inside diameter of the lubricant reservoir 8is larger than that of the other portion of the cylindrical hole 2 toinsure the quantity of a lubricant enough for improving the durability).Thus, the radial bearing surface 6 is not affected. In the bearingmember 4, since the portion for firm insertion is thinner than the otherportion, the affection of the pressure in the axial direction can bedecreased. Thus, the bearing member 4 can be fixed to the housing 3 byfirm insertion without decreasing the required accuracy of the radialbearing surface 6.

Since the accuracy of the outside diameter of the bearing member 4 isrequired merely at the portion 4c (small diameter portion) near theopening for firm insertion, the processing of the bearing member 4 iseasy.

Other operations and effects are similar to those of the thirdembodiment.

FIG. 5 shows the fifth embodiment.

Features different from the third embodiment are that there is nohousing and the bearing member 4 made of resin is directly fixed to theinner circumferential surface of the stator 9 which is an annular memberas shown in FIG. 6. The flange 21 of the lower portion of the bearingmember 4 is sandwiched and pressed by the stator 9 and the base 10 andis fixed to the stator 9 and the base 10 with a screw 11. The upperportion and the middle portion of the bearing member 4 are directlyfixed to the stator 9 by adhesion. There are advantages that the numberof parts is decreased and assembling becomes easy.

Other operations and effects are similar to those of the thirdembodiment. The stator 9 which constitutes the drive mechanism of themotor 1 including the hydro-dynamic fluid bearing device, is an annularmember made of steel. The rigidity of it is larger than that of thebearing member 4 made of resin. The inner circumferential surface of thestator 9 is annular.

FIG. 7 shows the sixth embodiment.

Features different from the fifth embodiment are that a filler 30 isdisposed in a gap between the upper portion of the outer circumferentialsurface of the bearing member 4 and the inner circumferential surface ofthe stator 9 so as to fix the stator 9 and the bearing member 4 to eachother. Although the bearing member 4 and the stator 9 are not fixed toeach other by adhesion, the bearing member 4 can be sufficientlyreinforced by filling the gap between the bearing member 4 and thestator 9 with the filler 30.

Other operations and effects are similar to those of the fifthembodiment.

This embodiment is not restrictive, and the bearing member 4 may bereinforced by the manner that two portions of both end portions in theaxial direction of the outer circumferential surface of the bearingmember 4 are fixed to an annular member the rigidity of which is largerthan that of the bearing member 4.

The present invention may be a combination in which some of the first tosixth embodiments are combined in an ordinary manner. The outercircumferential surface of the bearing member 4 may be reinforced by themanner that it is mounted to the rotor 14 which is an annular membermade of steel and constitutes the drive mechanism of the motor includingthe hydro-dynamic fluid bearing device. The rigidity of the rotor 14 islarger than that of the bearing member 4 made of resin. In that case,the bearing member 4 rotates.

The bearing member 4 in which the radial bearing surface 6 havinggrooves 5 for generating hydro-dynamic fluid requires a high accuracy ismanufactured by injection molding. If the flange 21 extending outwardsin the radial direction from the outer circumferential surface of thebearing member 4 is positioned at the same level of the portion 4c nearthe opening of the cylindrical hole 2 or the middle portion in the axialdirection, the inner circumferential surface of the cylindrical hole 2can not be accurately formed due to sink marks by the influence of thedifference of the thickness in the radial direction of the bearingmember 4. Therefore, the flange 21 is formed at the level near thebottom portion of the bearing member 4. The influence of the differenceof the thickness of the bearing member 4 which the inner circumferentialsurface of the cylindrical hole 2 receives is thus decreased so theinner circumferential surface of the cylindrical hole 2 is accuratelyformed. The rigidity of the bearing member 4 increases by the mannerthat the bearing member 4 is fixed to the annular member. The bearingmember 4 is not provided with the flange 21.

Next, FIG. 8 shows a cross-sectional view of a bearing device accordingto the seventh embodiment of the present invention. A rotational memberincludes a shaft 101, a disk attachment flange 106 and a rotor 103. Asupporting member for supporting the rotational member includes a stator104, a base 102 and a bearing member 105.

Because the fundamental structure of the rotational member is the sameas that of the prior art bearing device shown in FIG. 12, thedescription will be omitted. As the quality of the material for theshaft 101 in the bearing device according to this embodiment, astainless steel of SUS 440C treated by heat which is generally used isemployed. But the quality of the material for the shaft 101 used in abearing device of the present invention is not limited if the conditionof the diameter of 2 to 5 mm of the shaft which is a necessary conditionof the present invention is satisfied.

The fundamental structure of the supporting member for supporting therotational member is also the same as that of the prior art bearingdevice shown in FIG. 12. But, since the shape and so on of the bearingmember differ from those of the prior art bearing device, those pointswill be mainly described.

In the bearing device of the present invention, a flange 105c of thebearing member 105 is disposed below a cylindrical portion of thebearing member 105. Thus, in the bearing member, the positions in theaxial direction of the portion of the grooves for generatinghydro-dynamic fluid and the flange are different from each other. Bythis structure, at the injection molding of the bearing member of resin,it is prevented to decrease the accuracy of the portion of the groovesfor generating hydro-dynamic fluid due to an influence of the flange105c.

In the prior art bearing device, the thrust bearing surface of thethrust bearing is formed by the manner that a steel ball which is thethrust receiving member is tightly inserted in the bearing member. But,in the present invention, the bearing member 105 is provided with thethrust bearing surface, the central portion of which is a convexspherical surface 105d.

By this structure, the convex portion can be formed in the bearingdevice at the same time as the injection molding of the bearing memberof resin. Thus, the process of inserting tightly the steel ball for thethrust receiving member in the bearing member can be omitted so itbecomes possible to improve the workability of assembling.

A base 102 made of metal such as aluminum die cast and zinc die cast isused. As shown in FIG. 8, the cylindrical portion 105e of the bearingmember 105 is fixed on a cylindrical portion 102a of the base 102. Theflexural rigidity of the bearing member 105 made of synthetic resin isthus strengthened. In this case, particularly, since the longcylindrical portion 102a of the base 102 is disposed along thecylindrical portion 105e of the bearing member, the flexural rigidity ofthe bearing member 105 made of synthetic resin is strengthened.

In the bearing device of the present invention, for strengthening theflexural rigidity of the bearing member of the fluid bearing, it is alsopossible that the cylindrical portion 105e having the radial bearingsurface of the bearing member is made of copper group metal such asfree-cutting brass and phosphorus bronze, and a thrust receiving memberhaving a thrust bearing surface is fixed to the bearing member. Thethrust receiving member may be a thrust plate made of ceramics or thelike. In this structure, the strength of the flexural rigidity of thebearing member 105 can be insured even without a long cylindricalportion 102a of the base 102.

When an adhesive fills up between the cylindrical portion 105e of thebearing member and the cylindrical portion 102a of the base, theflexural rigidity of the bearing member 105 becomes stronger. Thesupporting member for supporting the rotational member is completed bythe manner that a stator 104 is assembled in the cylindrical portion102a of the base by firm insertion or the like.

Next, the structure of the cylindrical portion 105e of the bearingmember will be described. In the inner circumferential surface of thecylindrical portion 105e of the bearing member, radial bearing surfaces105a are formed at two portions which are distant from each other in theaxial direction. Herringbone-shaped grooves for generating hydro-dynamicfluid are formed in each radial bearing surface 105a. A shaft 101disposed in the bearing member 105 has cylindrical radial receivingsurfaces 101a which are opposite to the radial bearing surfaces 105athrough a lubricant in a radial bearing gap 107, respectively.

The radial bearing gap 107 is established so as to meet the condition of3.5 to 10 μm which is a necessary condition of the present invention. Ifit is out of the range, the load capacity becomes small or the dynamictorque becomes large.

The lower end surface of the shaft 101 has a thrust receiving surface101b opposite to a thrust bearing surface 105b through the lubricant.The thrust bearing surface 105b is a convex spherical surface so as tobe in a point contact with the thrust receiving surface 101b fordecreasing the contact area between them.

A fluoric oil which has the kinematic viscosity of 20 to 200 cSt at 40°C. is disposed as a lubricant between the radial bearing surface 105aand the radial receiving surface 101a and between the thrust bearingsurface 101b and the thrust receiving surface 105b.

Next, the operation of the bearing device of the present invention willbe described. But since the fundamental operation is the same as that ofthe prior art bearing device, an outline of the operation will be merelydescribed. When the stator 104 is electrified, a rotating magnetic fieldis generated. The rotor 103 thereby rotates together with the shaft 101and the disk attachment flange 106. When the rotational memberconstituted by the shaft 101, the rotor 103 and so on rotates, thethrust bearing surface 101b rotates in point contact state with thethrust receiving surface 105b through the lubricant.

The thrust bearing surface 101b and the thrust receiving surface 105bconstitute a sliding bearing by such point contact. At this time, sincethe lubricant flows in the thrust bearing gap 108 between the thrustbearing surface 101b and the thrust receiving surface 105b, and they arein point contact with each other through the lubricant, the boundarylubrication properties are improved to decrease the abrasion of thethrust bearing surface 101b and the thrust receiving surface 105b.

While the thrust receiving surface 105b is in point contact with thethrust bearing surface 101b and rotates relatively to the latter, thepressures of the lubricant in the radial bearing gaps 107 between theradial bearing surfaces 105a and the radial receiving surfaces 101aincrease because of a pumping effect by the grooves for generatinghydro-dynamic fluid, respectively. The radial bearing surfaces 105arotate in non-contact state with the radial receiving surfaces 101a.Although the rotational operation starts, in the case of the structureof the bearing device of the present invention, the flexural rigidity ofthe shaft can be insured and it becomes possible to suppress theincrease of the torque at a low temperature.

For improving boundary lubrication properties and leakage properties ofthe lubricant, the fluoric oil includes perfluoropolyether having acarboxylic acid at its termination which is mixed by 0.1 to 10 wt. %.

In the bearing device of the present invention, considering the lack ofcorrosion resistant properties of fluoric oil, stainless steel is usedas the material of the shaft and plastics is used for the bearingmember. For improving the slidability at the time of start and stop, PPS(polyphenylene sulfide resin) including carbon fibers and Teflon can beused as the material of the bearing member. In this invention, taking itthe other way round, it is also possible to rotate the bearing member105 which is born by the shaft 101.

The eighth embodiment of the present invention is shown in FIG. 9.

FIG. 9 is a vertically cross-sectional view of a hydro-dynamic fluidbearing member 310 according to the present invention in which theradial bearing and the thrust bearing are integrated with each other.

First, the structure will be described. In the hydro-dynamic fluidbearing member 310, a cylindrical portion 307 and a bottom portion 308integral with the cylindrical portion 307 are formed into one body of aresin material by injection molding. A cylindrical bearing hole 310a thecentral axis of which extends in the vertical direction is formed insideof the hydro-dynamic fluid bearing member 310. The upper end of thebearing hole 310a is open to communicate the exterior. The lower end ofthe bearing hole 310a is closed to form a bottom surface. A flange 310bprovided with through holes 310c for bolts which are utilized when astator and so on are fixed to the hydro-dynamic fluid bearing member 310is formed integrally with the outer circumferential surface of thebottom portion 308 of the hydro-dynamic fluid bearing member 310.

In the inner circumferential surface of the bearing hole 310a,cylindrical radial bearing surfaces 312 are formed at two portions whichare distant from each other in the axial direction. Grooves 311a and311b for generating hydro-dynamic fluid are formed in the radial bearingsurfaces 312, respectively. Thus the cylindrical portion 307 has thegrooves 311a and 311b for generating hydro-dynamic fluid in the innersurface. Both ends of the radial bearing surfaces 312 in the radialdirection (vertical direction in FIG. 9) are respectively connected tooil reservoirs 314a, 314b and 314c of annular groove shapes which areutilized for improving the durabilities of the radial bearing surfaces312 by supplying an oil as a lubricant fluid to the radial bearingsurfaces 312. These oil reservoirs 314a, 314b and 314c are continuous inthe circumferential direction, respectively. The oil reservoirs 314a and314b communicate with the upper and lower ends of the grooves 311a forgenerating hydro-dynamic fluid, respectively. The oil reservoirs 314band 314c communicate with the upper and lower ends of the grooves 311bfor generating hydro-dynamic fluid, respectively.

At injection molding, the oil reservoirs 314a, 314b and 314c and thegrooves 311a and 311b for generating hydro-dynamic fluid are separatedby forced drawing from a core pin which formed them. Thus, the depth h1of the oil reservoirs 314a, 314b and 314c is nearly equal to the depthh0 of the grooves 311a and 311b.

In the present invention, also the oil reservoirs can be easily formed.For instance, they can be formed in the hydro-dynamic fluid bearingmerely by processing protruded portions for forming the oil reservoirs,on the outer circumferential surface of a cylindrical core pin inaddition to protruded portions for forming the grooves for generatinghydro-dynamic fluid.

At the time of injection molding of resin, the portion near the openingend of the bearing hole 310a and the portion near the flange 310b of theinner circumferential surface of the cylindrical portion 307 are apt tobe affected by orientation properties and the rate of solidification incomparison to the other portion of the inner circumferential surface ofthe cylindrical portion 307. Thus, those portions are apt to be inferiorin the molding accuracy to the other portion of the innercircumferential surface of the cylindrical portion 307. Accordingly, byforming the oil reservoirs which are not so required the processingaccuracy are formed in such portions as apt to inferior in the moldingaccuracy, the problems of the processing accuracy can be solved and thequantity of the lubricant enough for improving the durability isinsured.

As for dimensions of the hydro-dynamic fluid bearing member 310according to this embodiment, considering the accuracy and the strength,the inside diameter of the cylindrical portion 307 is 3 mm, the outsidediameter is 5.5 mm and the thickness is 1.25 mm. The length in the axialdirection of the hydro-dynamic fluid bearing member 310 is 12 mm, andthe depth of the bearing hole 310a is 10 mm. The thickness of the flange310c is 1.5 mm in consideration of the strength at the fixture.

FIG. 10A shows measurement data of the roundness. In the drawing, 10Arepresents a measurement result of the roundness where the insidediameter surface of the cross-section of the cylindrical portion of thehydro-dynamic fluid bearing member along a line 10A--10A in FIG. 9 ismeasured. 10A' represents a measurement result of the roundness wherethe inside diameter surface of the cross-section of the cylindricalportion of the hydro-dynamic fluid bearing member along a line10A'--10A' in FIG. 9 is measured. It is realized that the roundness isless than 2 μm in either of 10A and 10A'. FIG. 10B shows results wherethe shape of the bearing hole of the cylindrical portion of thehydro-dynamic fluid bearing member is measured in the axial direction.In the drawing, 10B and 10B' represent results from points 10B and 10B'in FIG. 9, respectively, where the shape of the inside diameter surfaceis measured in the axial direction from the bottom portion to theopening end along the inside diameter surface of the bearing hole. Thedepth of the grooves for generating hydro-dynamic fluid and the depth ofthe oil reservoirs are 9 to 11 μm and the accuracy of the depth is lessthan 2 μm. The accuracy of the shape is less than 2 μm throughout theinside diameter surface. As realized from the above results, as foreither of the roundness and the shape, the hydro-dynamic fluid bearingaccording to the present invention satisfies enough the necessaryaccuracy for hydro-dynamic fluid bearing.

When the inside diameter of the cylindrical portion 307 is 2 to 5 mm andthe thickness of the cylindrical portion 307 is 0.8 to 2.0 mm, a nearlyequal accuracy could be obtained.

Since the hydro-dynamic fluid bearing is superior in the slidability andthe durability, it is possible to reduce impacts and damages whentouching the shaft at the time of start and stop. The wear resistance ofthe bottom portion which is especially apt to suffer abrasion issuperior.

In the case of forming two herringbone patterns of grooves as a groovepattern formed in the cylindrical portion 307 constituting the radialhydro-dynamic fluid bearing as the embodiment, non-symmetric grooves maybe formed so that the widths a' and b' in the axial direction outside ofbending portions are larger than the widths a and b in the axialdirection inside of the bending portions, respectively. By pumpingeffects of such non-symmetric grooves, even if the dimensional accuracyor the shape of the inner surface of the cylindrical portion is slightlybad, the flow of a lubricant fluid is forcedly introduced to the middleportion of the hydro-dynamic fluid bearing. Thus, the lubricant fluid isprevented from leaking out of the hydro-dynamic fluid bearing so it isdesirable for insuring the durability. The groove pattern is not limitedto the embodiment. It may be one herringbone pattern. A pattern orpatterns other than the herringbone pattern may be used. Since thegroove pattern can be determined merely in accordance with the patternof protrusions for forming grooves for generating hydro-dynamic fluid,which is processed in a core pin of a mold for forming the bearing hole310a, any pattern can be easily manufactured.

In the bottom portion 308 constituting the thrust bearing portion, thecentral portion of the thrust bearing surface 313 of the bottom surfaceof the bearing hole 310a is formed into a convex spherical surface.Since it is in point contact with the end surface of the shaft insertedin the bearing hole 310a, the friction torque at a rotation is kept fromincreasing. In the case of a large axial load, grooves for generatinghydro-dynamic fluid may be formed in the thrust bearing surface 313 soas to generate a lifting force by a hydro-dynamic fluid effect attendingon rotation. The abrasion of the thrust bearing surface is therebyreduced. A protrusion having a flat surface at the top may be formed inthe thrust bearing surface 313 in place of the convex spherical surface.It is also possible that the thrust bearing surface 313 is flat and theend surface of the shaft opposite to the thrust bearing surface 313 isspherical. After all, the thrust bearing surface 313 can have any shapeif the friction is low when rotating and the partial contact with theshaft can be avoided. Similarly in the case of manufacturing the groovepattern of grooves for generating hydro-dynamic fluid or the oilreservoirs, since the shape of the thrust bearing surface 313 can beselected merely by processing an end surface of a core pin of a mold forforming the bearing hole 310a, any shape can be easily manufactured.

FIG. 11 shows an instance of a mold for injection molding for amanufacturing method of a hydro-dynamic fluid bearing of the presentinvention (a vertically cross-sectional view of the principal part).

The mold is a three-plates mold. The fixed side comprises a spoor bush421, a fixed side attachment plate 423 to which a runner lock pin 422 isattached, a runner stripper plate 424, a fixed side mold plate 426having a fixed side cavity 425, and so on. The fixed side cavity 425 isprovided with a runner 427, a gate 428 and a recessed portion 425a forforming a bottom portion of a hydro-dynamic fluid bearing.

The movable side comprises a movable side mold plate 430 having amovable side cavity 429, and so on. The movable side cavity 429 isprovided with recessed portions 429a and 429b for forming a flange and acylindrical portion of a hydro-dynamic fluid bearing, respectively.Further, there is provided a core pin 431 for forming a radial bearingsurface, which has grooves for generating hydro-dynamic fluid, of acylindrical portion of a hydro-dynamic fluid bearing, and a thrustbearing surface 313, which is connected to the radial bearing surface,of a bottom portion of the hydro-dynamic fluid bearing.

The other parts of the movable side (a guide pin, a support pin, aspacer block, a movable side attachment plate, an ejector plate to whichan ejector pin is attached, a return pin, a spring and so on) and atension link for operating the three plates, a plug bolt, a stop bolt, aheater for controlling the temperature of the mold, and so on areomitted in the drawing.

When a hydro-dynamic fluid bearing is formed by injection molding usingthe above mold, molten resin injected from an injection nozzle of aninjection molding machine into the mold flows through a spoor 432 andthe runner 427 and flows into the recessed portion 425a, which is formedin the fixed side cavity 425, for forming a bottom portion of thehydro-dynamic fluid bearing, from the one point pinpoint gate 428provided nearly at the center of the recessed portion 425a. The resinflowing into the recessed portion 425a is filled in the recessed portion425a. The resin is then filled in the recessed portion 429a of themovable side cavity 429 uniformly in the circumferential direction ofthe recessed portion 429a. After this, the resin is filled in therecessed portion 429b. Since the resin is filled from the one pointpinpoint gate 428 nearly at the center of the recessed portion 425a,when filling in the recessed portion 429b for forming a cylindricalportion of the hydro-dynamic fluid bearing, the leading portion of themolten resin flows to the axial direction of the recessed portion 429buniformly in the circumferential direction. Thus, no weld mark isgenerated and the injection pressure is applied uniformly. The nearlycentral portion 440 of the outer surface of the bottom portion of thehydro-dynamic fluid bearing is the portion that the resin materiallastly flows in the mold at the injection molding. Thus, a mark of gateremains. Since there is used the material for molding in which carbonfibers and one or more fillers other than the carbon fibers are filledto polyphenylene sulfide resin, the total content of the fillers is 20to 50 wt. %, and the melt index of the material is 4 to 9 g/min.(measured at the resin temperature of 300° C. and the load of 5 kg),high accuracies (the roundness, the generant shape, the cylindricaldegree, and the dimensional accuracy) can be obtained.

After keeping pressure and cooling, by the separation of the mold of themolding machine, the mold is opened between the fixed side mold plate426 and the runner stripper plate 424. The portion of the gate 28 is cutso that a hydro-dynamic fluid bearing (product) remains in the fixedside cavity 429, and a spoor and a runner remain on the runner stripperplate 424. Next, the mold is opened between a PL (parting line) 433 andthe runner stripper plate 424 and between the runner stripper plate 424and the fixed side attachment plate 423. The separation of thehydro-dynamic fluid bearing from the movable side cavity 429 isperformed by the manner that the flange surface is pushed out by theejector pin 434. Thus, grooves for generating hydro-dynamic fluid areseparated from the core pin 431 which formed the grooves for generatinghydro-dynamic fluid, by forced drawing by utilizing the elasticdeformation of resin. Since the grooves for generating hydro-dynamicfluid are separated from the core pin to the axial direction by forceddrawing, the structure of the mold can be simplified. Since the shapeand the pattern of the grooves for generating hydro-dynamic fluid can bedetermined merely by processing the corresponding shape and pattern tothe core pin, the freedom of the design of the grooves for generatinghydro-dynamic fluid increases.

The position for pushing out a hydro-dynamic fluid bearing is notlimited to this embodiment. The end surface around the opening of thehydro-dynamic fluid bearing may be pushed out by an ejector pin or asleeve.

What is claimed is:
 1. A hydro-dynamic fluid bearing device comprising acylindrical shaft, a substantially cylindrical bearing member foraxially supporting the shaft rotatably in a cylindrical hole having abottom surface, a supporting member fixed on one side of the shaft andthe bearing member, and a rotation member fixed on the other side of theshaft and the bearing member and rotatably supported on the supportingmember, grooves for generating hydro-dynamic fluid being formed on atleast one of the outer peripheral surface of the shaft and the innerperipheral surface of the cylindrical hole of the bearing member,whereinthe bearing member is made of a resin material, and the outerperipheral surface of the substantially cylindrical portion is fixed toan annular reinforcing member having a higher rigidity than the bearingmember.
 2. A hydro-dynamic fluid bearing device according to claim 1,wherein said annular reinforcing member is fixed on said supportingmember by using a flange portion included in said annular reinforcingmember and an inner surface of a cylindrical portion of said annularreinforcing member is adhered to said outer peripheral surface of saidbearing member.
 3. A hydro-dynamic fluid bearing device according toclaim 2, wherein said bearing member includes a flange for being fixedon said supporting member.
 4. A hydro-dynamic fluid bearing deviceaccording to claim 1, wherein a diameter of said outer peripheralsurface of said bearing member is smaller at a portion near an openingof said cylindrical hole than at other portion, said portion being fixedto said inner surface of said cylindrical portion of said annularreinforcing member by adhesion or firm insertion.
 5. A hydro-dynamicfluid bearing device according to claim 4, wherein said annularreinforcing member is fixed on said supporting member by using a flangeportion included in said annular reinforcing member.
 6. A hydro-dynamicfluid bearing device according to claim 5, wherein said bearing memberincludes a flange for being fixed on said supporting member.
 7. Ahydro-dynamic fluid bearing device according to claim 6, wherein afiller is disposed in a gap between an upper portion of an outercircumferential surface of said stator.
 8. A hydro-dynamic fluid bearingdevice according to claim 1, wherein said annular reinforcing member isa stator and said bearing member includes a flange for being fixed onsaid supporting member.